Seed priming

ABSTRACT

A method for treating plant seed is provided comprising contacting them with a first surface of semi-permeable membrane having first and second surfaces, the second surface being in direct contact with a solution of predetermined osmotic potential, whereby the seeds abstract water from the solution through the membrane, wherein the seed and semi-permeable membrane are constantly or periodically caused to move relative to each other such as to constantly or periodically reorient the seed with respect to the first surface such that the transfer of water occurs evenly over substantially the entire surface area of the seed.

This is a continuation of application Ser. No. 08/809,104, filed Mar.17, 1997, now U.S. Pat. No. 5,873,197 which is a 371 of PCT/GB95/02188filed Sep. 15, 1995.

The present invention relates to a method of treating seeds bycontrolling their water content, particularly to priming and/orgerminating seeds or inducing desiccation tolerance in them. Theinvention further provides seeds primed, germinated or made desiccationtolerant by the method of the invention and to an apparatus forperforming the method.

BACKGROUND OF THE INVENTION

Seed priming is a process for treating plant seeds that enables them toundergo faster and more uniform germination on sowing or planting, withthe option of simultaneously treating them with fungicide or otherpreservatives providing protection during processing or after sowing andallowing their prolonged storage, e.g. in packets displayed at point ofsale.

This process allows the seeds to absorb enough water to enable theirpre-germinative metabolic processes to begin and then arrests them atthat stage. The amount of water absorbed must be carefully controlled astoo much would simply allow the seed to germinate and too little wouldresult in the seed ageing. Once the correct amount of water has beenabsorbed it is then necessary to hold the seed at that water content fora period, typically one to two weeks, before drying it back to theoriginal water content for storage. When subsequently sown the seedsusually germinate more quickly and uniformly than natural unprimed seedsand, where the geographical situation of the point of priming allows,the seeds can be sown directly after priming without drying whereuponthey germinate even faster than those which have been primed and dried.

The conventional way of priming seeds has been to immerse them in anaerated solution of an osmotic material, usually polyethylene glycol(PEG). The seed coat is more or less semi-permeable to PEG such that theosmotic potential of the seed tends to equilibrate with that of thesolution; the PEG concentration being chosen such that it will not allowseed to absorb enough water to germinate. This works well for manyspecies but the priming of large quantities of seed requires largequantities of PEG solution and this can cause disposal problems,particularly if fungicides have been added. Immersion in liquid alsorestricts oxygen absorption and some seeds, particularly onions, willonly prime satisfactorily if the solution is aerated using air enrichedwith oxygen.

To avoid the problems of large scale priming with PEG the system knownas `drum priming` was devised (see U.S. Pat. No. 5,119,598=GB 2192781).This involves first carrying out tests on a seed lot to determine theoptimum level of hydration and then hydrates the bulk of seeds in a drumwhich is slowly rotated about its horizontal longitudinal axis. Water isadded to the drum more slowly than the seeds are able to absorb so thatthey become hydrated without ever appearing to get wet. The seeds arenext incubated in a revolving drum with access to air for a periodappropriate to their type before drying.

An alternative method of priming seeds is known as `matrix priming` anddoes not involve the use of PEG but utilises an absorbent medium such asclay or peat to absorb water and then transfer it to the seeds (see U.S.Pat. No. 4,912,874). The extent of seed hydration is controlled byaltering the water content of the medium and the medium/seed ratio. Theprocess is completed by removal of seed from the medium with optionaldrying. Both drum and matrix priming have been developed to avoid theproblems of using PEG when priming large quantities of seed.

Further seed treatments involving control of seed water content aregermination and desiccation tolerance induction treatments. Treatmentfor producing germinated seeds may involve treatment similar to primingas described above with treatment being continued until the radicleemerges. Seed so produced may be further dried back and/or coated asdescribed in U.S. Pat. No. 4,905,411. Separation of the germinated seedfrom primed seed may be carried out using a seed classifier operating toseparate seeds showing signs of radicle emergence from those that donot. Such apparatus and method are exemplified by the disclosure ofKirin Brewery Co Ltd JETRO May 1994 where a video CCD camera is used toobserve seed for colour and size of tissue and a compressor device isused to move selected developed seed from undeveloped seed. Treatmentfor induction of desiccation tolerance in seed with emerged radicles isexemplified by WO 94/05145 wherein the content of the seed is heldbetween 35 and 55% weight such that the emerged radicle does not developwhile other metabolic processes continue.

SUMMARY OF THE INVENTION

The present invention provides a further method and apparatus forcontrolling the water content of seeds that does not require constantactive addition of water, as required in conventional drum priming, bututilises a semi-permeable membrane to mediate the transfer of water froma solution of set osmotic pressure to the seed. The use of this methodallows for the set up of automated forms the apparatus for performingthe method. The invention also concerns itself with requirements oftreating small quantities of seeds simultaneously in multiple lots, suchas required when priming high value flower seeds of different varieties,with the advantages of drum priming over matrix priming with respect toseparation of seeds post treatment.

Particular advantages are provided in using the present method andapparatus to treat seeds having mucilaginous coats, for example thosesuch as Pansy and Salvia seeds; and especially to prime such seeds.These seeds do not respond well to other water treatment methods, eg.priming methods, as the mucilage layer becomes swollen with water andrestricts gas exchange necessary for pre-germination and seeddevelopment.

Semi-permeable membrane apparatus has been reported as being used formodelling water stress on seed germination in a seedbed (see Rowse et al(1986) Rep. Natn. Veg. Res. Stn. for 1985) wherein seeds were germinatedbetween a ceramic plate and a semi-permeable bag of PEG solution, withfurther development by Fyfield et al (1989) J. Experimental Botany, Vol.40, no 215, pp667-674. This latter work was not directed at productionof seed for drying back and/or packaging but concerned itself withdetermining the ideal conditions for radicle emergence in mungbeanseeds.

In a first aspect of the present invention there is provided a method oftreating a seed to effect control of its water content comprisingcontacting the seed with a first surface of a semi-permeable membranehaving first and second surfaces, the second surface being in directcontact with a solution of predetermined osmotic potential such that theseed abstracts water from the solution through the membrane, wherein theseed and semi-permeable membrane are constantly or periodically causedto move relative to each other such as to constantly or periodicallyreorient the seed with respect to the first surface such that thetransfer of water occurs evenly over substantially the entire surfacearea of the seed.

In a preferred method of the first aspect of the present invention theiris provided a method for priming or germinating or inducing desiccationtolerance in a seed wherein the solution of predetermined osmoticpressure is such as to allow the seed to abstract water from it throughthe semi-permeable membrane; the period for which the seed is treatedbeing sufficient to allow pre-germinative metabolic processes to takeplace within the seed up to any level including that immediatelypreceding radicle emergence for priming, up to radicle emergence forgermination and being insufficient to support radicle growth butsufficient to allow other metabolic processes to continue in the case ofdesiccation tolerance induction.

Preferably the seeds and semi-permeable membrane are caused to moverelative to each other such that the seeds are constantly reorientatedwith respect to the first surface whereby they take up water evenly overtheir entire surface areas, this particularly being effected by causingthe seed to roll or tumble across the membrane. More preferably thesemi-permeable membrane is provided in the form of a tube, e.g. ofpolygonal or circular cross-section, and this tube is rotated with theseeds on its inner surface and the solution retained between its outersurface and a further body, to which the membrane is sealed in awatertight manner or of which the membrane is an integral part.

The semi-permeable membrane is such that, when the second surface (i.e.the tube outer surface) is contacted with solution, the first surface(i.e. the tube inner surface) appears to be dry. It is preferred thatonly the contact of the seed, or some other intermediate absorbent body,with the first surface results in the transfer of water from the secondsurface. To facilitate retention of the seed within the confines of thetube of semi-permeable membrane in use, it is preferred to use the tubeformat with retaining elements, eg. caps placed at each end.

Most preferably the semi-permeable membrane is located on a frame withina drum device such that it divides the drum device into inner and outerchambers which are isolated with respect to water transfer between thetwo other than through the semi-permeable membrane itself. The secondchamber preferably is completed by one or more other non-permeable wallelements, preferably including that/those upon which the semi-permeablemembrane tube is mounted.

The semi-permeable membrane may be made from any material that ispermeable to water but impermeable to the solution of predeterminedosmotic pressure. Conveniently membranes are those of cellulose and/orpolycarbonate materials, with fungicide addition to the solution beingpotentially necessary where cellulose membranes are used to preventfungal growth on the membrane. Suitable types of membrane include thatused for dialysis, e.g. for visking dialysis.

When formed into a tube the membrane may take any cross-sectional formbut conveniently may be a simple form of, eg. circular or polygonal eg.square or hexagonal nature. The rate at which this tube is rotated withthe seed held in its inner volume will vary with its diameter. The speedshould be sufficient to effect the reorientation of the seed withrespect to the surface, with no particular limitation being intended.Typically this is about 0.8 to 1.2 rpm for a 110 mm diameter unit.

The priming conditions with respect to osmotic potential will vary fromseed to seed with solutions providing between -0.5 to -2.0 MPa osmoticpotential typically being used for priming or germinating. Suitableosmotic potential for stressing seed to induce desiccation tolerancewill be determined by simple bench experimentation, but will be such asto produce a seed water level sufficient to inhibit radicle growth butsufficiently high to permit other metabolic processes to continue, eg.providing a water content of 35 to 55% by weight of the seed. Preferredconditions will be consistent with those disclosed in WO 94/05145.

The preferred temperature at which the method of the invention iscarried out may vary with the seeds to be treated, but is typicallybetween 10 and 25° C., more preferably between 15 and 20° C. for primingand desiccation tolerance induction, and optionally up to as much as 40°C. for germination. Such temperature control is conveniently achieved bycarrying out rolling of the tube within a drive frame mounted within atemperature controlled environment, e.g. in a temperature controlledroom.

Using the preferred tubular membrane method of the present inventionwherein inner and outer chambers contain a number of seeds and solutionof predetermined osmotic potential respectively, advantages are providedwherein seeds are constantly mixed such that equal access to the watersupplying membrane is offered, the osmotic solution (e.g. aqueous PEGsolution) is constantly agitated or stirred to minimize concentrationgradients that would otherwise build up as water is taken across themembrane, and temperature gradients are prevented which might otherwiseallow pure water to distil onto cooler parts of the unit and thus allowseed to take up too much water at one contact point.

In a second aspect of the present invention there is provided apparatusfor performance of the method of the invention, this comprising asemi-permeable membrane having first and second surfaces, the firstsurface being adapted to be in contact with a seed to be treated in use,the second surface being located in a chamber adapted to contain asolution of predetermined osmotic potential in contact with the secondsurface such that in use the seed is able to abstract water from thesolution through the membrane wherein the apparatus is adapted such thatin use the first surface and seed may be caused to move relative to eachother such that the seed is periodically or constantly reorientated withrespect to the first surface whereby the transfer of water takes placeevenly over its entire surface area.

The semi-permeable membrane is preferably provided in the form of a tubeof circular or polygonal cross-section which is rotatable such as to becapable of carrying the seed on its inner surface with the solutionretained in the chamber which is formed between its outer surface and afurther body to which the membrane is sealed in a watertight manner. Therelative movement of the first surface and the seed preferably inducesrolling and tumbling motion of the seed across the surface.

Preferably the semi-permeable membrane is such that, when the tube outersurface is contacted with solution, the tube inner surface appears to bedry, particularly wherein only the contact of the seed or some otherabsorbent body with the first surface results in transfer of water tothe first side. The tube is conveniently provided with end caps. Mostconveniently the semi-permeable membrane is located on a support frame,eg. a tubular frame, within a drum device such that it divides the drumdevice into inner and outer chambers which are isolated with respect towater transfer between the two other than by through the semi-permeablemembrane itself. In such an embodiment the outer chamber is convenientlycompleted by other non-permeable wall elements including those uponwhich the semi-permeable membrane tube is mounted. The semi-permeablemembrane is made from any material that is permeable to water butimpermeable to the solution of predetermined osmotic pressure.Preferably the semi-permeable membrane is made from cellulose and/orpolycarbonate material suitable for dialysis.

In a particularly preferred embodiment of the invention the tube ismounted with its longitudinal axis substantially horizontally orientedin a drum device which is in turn mountable in a roller frame such thatit may be driven to rotate and thus cause the tube to rotate about itslongitudinal axis. Thus a preferred embodiment of the second aspect ofthe present invention provides the apparatus described above togetherwith a means for rotating it about its horizontally orientedlongitudinal axis, this drive means preferably comprising a power drivenroller frame.

It will be realised by those skilled in that art that the individualseeds, when applied in quantity to the chamber formed by the membraneinner surface, may not abstract their water directly from thesemi-permeable membrane but from adjacent seeds. As long as such seedsare periodically or continuously reorientated such that even waterdistribution is achieved such mechanism is contemplated as suitable forthe purposes of the present invention. Thus no limitation is intended onthe method of action on all of the seeds, other than one or some of theseeds at least should directly contact the membrane.

The method, apparatus and seeds of the invention will now be describedby way of illustration only by reference to the non-limiting Figures andExamples below. Further embodiments falling within the scope of theinvention will occur to those skilled in the art in the light of these.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: shows a cutaway perspective view of a drum mounted membraneapparatus according to the present invention as described in Example 1.

FIG. 2: shows a cross-sectional view, as viewed from the side, of thedrum mounted membrane apparatus shown in FIG. 1.

FIG. 3: shows an axial end view of the drum mounted membrane apparatusof FIG. 1 as mounted for rotation on a driven roller frame.

FIG. 4: shows a cutaway perspective view of the alternative embodimentof the apparatus of the invention of Example 2.

FIG. 5: shows a cross-section through the end of the apparatus ofExample 2 as viewed with the longitudinal axis horizontally oriented.

FIG. 6: shows a view of the closure and annuli of the apparatus ofExample 2 as viewed in the direction of the arrows provided in FIG. 5.

EXAMPLE 1 Apparatus of the Invention

A priming apparatus of the invention as shown in FIGS. 1 to 3 consistsof a drum formed of two concentric cylinders; an inner PVC cylinder (1)being a rigid and highly perforated tube on which a flexiblesemi-permeable membrane tube (2) is supported in use, and an outerunperforated PVC cylinder (3). Perspex closures (4) are provided ateither end of the inner cylinder and seal a solution of set osmoticpotential into the chamber (5), formed between the outer cylinder (3)and the membrane (2), and retain seed in the inner chamber (6), with theinterface provided by 2 mm sheet rubber gaskets (7). Seeds are placed inchamber (6) formed by the inner surface of the membrane (2). Membrane(2) is a tubular visking dialysis membrane with its diameter matched tothat of chamber (6) and made from cellulose; this being supplied byMedicell International Ltd., 239 Liverpool Road, London N1 1LX, UK. Forenabling rotation of the membrane relative to the seeds in use the drumis mounted upon a roller frame (Bellco cell production roller apparatus)using rubber rollers. Three sizes of drum of the invention are providedfor use in this frame, each having a different capacity for seeds; 25 gcapacity being 64 mm diameter by 58 mm length; 50 g capacity being 64 mmdiameter by 144 mm length and 100 g capacity being 81 mm diameter and210 mm length; all being inner cylinder dimensions. The inner cylinderis fixed in place in the outer cylinder via the fixed end cover (4a) andremovable end cover (4b) retained by a screw (8), bar (10) and wing nut(9). Screw (11) allows access to chamber (5) for replenishing watercontent of the solution while screw (8) has a central passage allowingtransfer of respiratory gases to and from the atmosphere.

EXAMPLE 2 Alternative Apparatus of the Invention

An alternative arrangement of an apparatus of the invention is shown inFIGS. 4 to 6. In FIG. 4 an outer PVC cylinder (12) and inner perforatedPVC cylinder (13) define between them an outer chamber (14) which isseparated from an inner chamber (15) with regard to liquid flow by asemi-permeable membrane tube (16) sourced as described in Example 1.

The inner cylinder is mounted in relation to the outer cylinder by wayof two part perspex annuli (17) which are in turn mounted on the outercylinder (12) via intermediate mounting elements (18) and screws (19a,19b, 20); the presence of two screws (19a and 19b) affixing elements(18) to the cylinder inhibiting movement of the element out of axialalignment with screws (20). Screws 20 carry o-rings (20a). The annuliconsist of front plates (17a) with back plates (17b) screwed onto themby screws (25) with annular sheet rubber gaskets (22) held between thetwo. Solution of predetermined osmotic potential is added to chamber(14) through one or both of two orifices plugged in use by screws (21)having o-ring seals (21a) about their shanks. These screws are accessedthrough throughholes (24) in end closures (23) The sheet rubber gaskets(22) reside between the annuli and the outer and inner cylinders (12)and (13) at each end of the apparatus for preventing leakage of solutionfrom the chamber. The semi-permeable membrane (16) is held taught acrossthe inner cylinder between the gaskets and the cylinder (13). The innerchamber (15) is closed by the perspex closures (23) at each end; thesebeing retained in place by nuts (27) which engage threaded metal lugs(28) projecting from the annuli or similar threaded mountings whichreleasably attach them to the annuli at each end. At least one of theclosures (23) has an air hole allowing passive exchange of respiratorygases between chamber (15) and the atmosphere.

EXAMPLE 3 Priming Method of the Invention

A number of drum devices of Example 1 or 2 were filled to between 33%and 50% of the volume of outer chamber (5, 14) with aqueous solutions ofPEG (molecular weight 20,000) to give osmotic strengths of between -0.6and -1.9 MPa as appropriate. The respective chambers (6, 15) were filledwith amounts of seeds dependent upon the capacity given in Example 1 andthe ends sealed with the closures (4, 23) mounted on the gaskets (7,22). The drums were placed with their outer cylinder side surfaces onthe rollers of a Bellco cell production roller apparatus (see FIG. 3) ina temperature controlled room at 15° C. and rotated at 0.8 rpm forperiods as described in the Table 2 below.

The water activity of the PEG solution was measured indirectly at setintervals, e.g. once a day, by weighing without seeds to determine thechange in water content of the outer chamber and adding water to restorethe original weight and thus osmotic pressure exerted. A computerprogram was used for operating numbers of units simultaneously whichrecorded details of each drum unit and controlled a peristaltic pump toadd correct amounts of water; water potential changes beingautomatically recorded.

The results obtained using this protocol are illustrated in Tables 1 and2: Table 1 giving the priming conditions used for a range of seeds usingthe method of the present invention and Table 2 giving results ofgermination tests for these and `natural`, ie. unprimed seeds.

                  TABLE 1                                                         ______________________________________                                        Priming conditions for fresh and dried primed                                 seeds of a range of species at 15° C.                                                       Fresh seed    Dry seed                                                        Potential     Potential                                  Species   Cultivar   MPa      Days MPa    Days                                ______________________________________                                        Coriander            -1.6     14                                              Sweet Fennel         -1.6     14                                              Sweet Marjoram       -1.7      9   -1.7    9                                  Dill                 -1.2     14                                              Sage                 -1.5     14                                              Parsley   Bravour                                                             Broccoli  Marathon   -0.6      4   -1.0    4                                  Broccoli  Arcadia    -0.8      5   -1.0    5                                  Tomato    Vibelco    -0.6      9   -0.6    9                                  Tomato    Rosella    -0.6      9   -0.9    9                                  Leek      Gavia      -1.4     12   -1.4   12                                  Pepper    Maestro 95 -0.9     18   -0.9   18                                  Pepper    Maestro 73 -0.9     18   -0.9   18                                  Pepper    Keystone RG                                                                              -1.0     14   -1.0   14                                  Pansy     Universal                -1.0    9                                  Primula   Paloma                   -1.2   14                                  Geranium  Colorama   -1.2     10   -1.4   10                                  Cyclamen  Rubin      -1.2     21                                              Celery    Victoria   -1.0     14   -1.4   14                                  ______________________________________                                    

As the present method may be used by large plant raisers for raisingplants under glass, a situation where production follows a fixed planand is not interrupted by bad weather, it was possible to consider useof undried, i.e. fresh-primed seed, which has limited shelf life as forsome species this produces faster and more uniform germination. Theperformance of these seeds is also given in Table 2.

Drying back after priming was carried out using standard techniques wellknown to those skilled in the art where required.

                                      TABLE 2                                     __________________________________________________________________________    Results of germination tests on seeds primed using MPa and times              set out in Table 1:                                                           Species Germ Temp                                                                           Natural Seed                                                                            Primed Fresh                                                                            Primed Dry                                  Cultivar                                                                              ° C.                                                                         % Germ                                                                            Days*                                                                             SD                                                                              % Germ                                                                            Days*                                                                             SD                                                                              % Germ                                                                            Days*                                                                             SD                                  __________________________________________________________________________    Coriander     89.8                                                                              5.3 3.5                                                                             100.0                                                                             0.5 0.4                                           Sweet Fennel  81.7                                                                              6.7 2.8                                                                             80.0                                                                              1.3 1.3                                           Sweet Marjoram                                                                              87.0                                                                              2.4 1.8                                                                             87.2                                                                              0.7 0.6                                                                             87.5                                                                              0.6 0.5                                 Dill          76.2                                                                              4.5 1.7                                                                             84.0                                                                              1.5 1.3                                           Sage          95.8                                                                              3.3 1.0                                                                             99.0                                                                              2.0 0.9                                           Parsley B                                                                             20-30 90.5                                                                              7.3 1.9                                                                             89.5                                                                              1.7 0.9                                                                             89.0                                                                              2.0 0.9                                 Broccoli M                                                                            15    99.5                                                                              2.3 0.3                                                                             98.4                                                                              1.0 0.5                                                                             9.5 1.8 0.6                                 Broccoli A                                                                            15    99.8                                                                              2.3 0.4                                                                             100.0                                                                             0.5 0.2                                                                             100.0                                                                             1.4 0.4                                 Tomato V                                                                              15    98.3                                                                              5.3 0.9                                                                             97.5                                                                              1.6 0.5                                                                             98.5                                                                              3.8 0.8                                 Tomato R                                                                              15    91.0                                                                              5.4 1.6                                                                             86.0                                                                              2.2 1.1                                                                             89.0                                                                              4.1 1.0                                 Leek G  15    92.8                                                                              4.2 1.1                                                                             96.0                                                                              0.8 0.8                                                                             92.3                                                                              1.9 0.6                                 Pepper M95                                                                            20-30 94.3                                                                              5.6 0.8                                                                             95.0                                                                              0.9 1.1                                                                             96.5                                                                              1.5 1.3                                 Pepper M73                                                                            20-30 94.8                                                                              5.4 1.4                                                                             82.5                                                                              1.1 1.2                                                                             89.5                                                                              1.6 1.2                                 Pepper KRG                                                                            20-30 99.3                                                                              4.5 1.4                                                                             98.0                                                                              0.7 0.6                                                                             98.7                                                                              1.5 0.6                                 Pansy U 20    91.0                                                                              5.0 2.1         83.4                                                                              2.1 0.9                                 Primula P                                                                             15    77.8                                                                              9.0 2.1         90.0                                                                              5.3 3.3                                 Geranium C                                                                            15    71.1                                                                              4.8 2.0                                                                             80.0                                                                              1.0 1.0                                                                             78.0                                                                              2.7 1.6                                 Cyclamen R                                                                            15    89.0                                                                              12.4                                                                              2.4                                                                             94.0                                                                              5.5 1.7                                                                             85.3                                                                              5.9 2.0                                 Celery V                                                                              20    87.8                                                                              6.8 1.9                                                                             92.8                                                                              1.0 0.8                                                                             90.5                                                                              2.9 2.0                                 __________________________________________________________________________     * = days to germination                                                  

Thus it can be seen from these results that dried Primula seeds havebeen provided that are capable of germinating in six days or less whiledried Pansy seeds obtained are capable of germinating in 60 hours orless.

EXAMPLE 4 Germination Method of the Invention

The method of Example 3 is used but the period for which the seed istreated is increased until at least some of the seeds show signs ofradicle emergence. Seeds are then transferred to a seed classifyingdevice of the type described by Kirin Brewery in JETRO May 1994 that hasbeen adapted by provision of hollow projections from the rotatingclassifier drum. These hollow projections are dimensioned such as tohave a distal end diameter less than the diameter of the seed and carrysuction generated by the blower such as to be capable of retaining theseed as the drum rotates past a seed reception zone.

The drum carried seeds are presented to a CCD camera which is used toprovide a signal or set of signals indicative of seed size and colourwhich is in turn used to classify seeds as germinated or ungerminated.Seeds classified as ungerminated are ejected by the reject nozzle andrecycled to the priming treatment of Example 3, while those classifiedas germinated are ejected at separate position, eg. by the scraperbrush, and further processed, eg. dried back, coated or rendereddesiccation tolerant, by treatment in a drum device of the inventionwhich utilises a solution of predetermined osmotic potential such as toproduce a seed water content between 35 and 55% by weight.

The criterion for classification of seed as germinated will convenientlyinclude the presence of a lighter colour visible on the seed surface dueto emergence of the radicle. The appropriate level of colour differencemay conveniently be determined by eg. discriminant analysis using seedof known germination status to set threshold values with a computerprocessor computing these for store in a memory device as is known inthe optical classifier art.

We claim:
 1. An isolated primed seed in which the seed has been providedwith a controlled water content for a sufficient period such as to allowmetabolic processes to take place within the seed up to the levelselected from the group consisting of(a) just prior to radicalemergence, (b) just after radical emergence, and (c) after radicalemergence but insufficient to support radical growth but sufficient toallow other metabolic processes to continue, wherein the seed isselected from the group having a mucilaginous coat which is capable ofbecoming swollen with water such that gas exchange necessary forpregermination and seed development is restricted.
 2. A seed as claimedin claim 1, wherein it is selected from the group consisting of Primula,Salvia and Pansy seeds.
 3. A seed as claimed in claim 1, wherein it is adried Primula seed capable of germinating in six days or less.
 4. A seedas claimed in claim 1, wherein it is a dried Pansy seed capable ofgerminating in sixty hours or less.